Space-based constraints on UK ammonia emissions and air quality impacts

We are offering an exciting PhD opportunity, in the School of Earth and Environment, to undertake novel research targeting one of the major air quality challenges facing the UK – the ammonia problem! Ammonia (NH3) is emitted primarily from diffuse agricultural sources and difficult to quantify for legislative purposes. Unlike other air pollutants, gaseous NH3 emissions have not decreased over recent decades and continue to promote extensive formation of ammonium nitrate aerosol – a hazardous air pollutant. Therefore, this project aims to exploit state-of-the-art satellite observations and modelling to better constrain NH3 emissions, their temporal changes (from a legislative point of view) and to quantify the impact of these emissions changes on key air pollutants such as PM2.5 (particulate matter with a diameter less than 2.5 microns).

Motivation

UK air pollution has a detrimental impact on our nation’s health and economy (e.g. healthcare, lost work hours). Despite substantial emission reductions of key pollutants (e.g. nitrogen oxides), the levelling off in ammonia (NH3) reductions since 2010 is a cause of serious concern for Department for Environment Food and Rural Affairs (Defra) and other government agencies. NH3 emissions are primarily from agricultural sources, which can result in secondary aerosol formation (i.e. ammonium nitrate) and contribute to hazardous levels of PM2.5. Environmental deposition of NH3-containing compounds can also cause significant long-term harm to sensitive habitats by increasing soil and water nitrogen concentrations. 

Defra uses the National Atmospheric Emissions Inventory (NAEI) to help inform air quality (AQ) policy including emissions of NH3. However, the NAEI is subject to large uncertainties; typically 50-100% for NH3. Here, satellite observations can provide a valuable constraint on atmospheric NH3 (e.g. UK-wide coverage) by helping to indirectly infer emission information (e.g. by mass balancing). Therefore, this studentship builds on previous work by using a nested regional atmospheric chemical transport model, novel satellite observations and the mass-balancing approach to derive robust top-down NH3 emissions over the UK. 

Methods, Models & Data

The global chemical transport model TOMCAT has been widely used for the atmospheric composition and air quality related research areas. Recent developments by UK National Centre for Atmospheric Science (NCAS) and National Centre for Earth Observations (NCEO) scientists of TOMCAT with a high horizontal resolution (i.e. < 10 km) nested grid, allows for targeted regional AQ studies (e.g. UK scale). NCAS and the Met Office have also developed a new flexible, stand-alone module of the UK Chemistry and Aerosols (UKCA – also used in the UK Earth System Model), which includes sophisticated NH3-nitrate aerosol interactions. This studentship will exploit both developments to undertake important and relatively computationally inexpensive UK regional simulations (i.e. unlike coupled UM-UKCA) to provide assessments of NH3 on aerosol formation and AQ impacts. 

New high quality satellite products from the Rutherford Appleton Laboratory (RAL), partially funded by NCEO, provide high-resolution and long-term (2008-present) records of NH3 from multiple sensors (e.g. Infrared Atmospheric Sounding Interferometer (IASI) and Cross-track Infrared Sounder (CrIS)). These satellite datasets can be combined with TOMCAT using the well-established mass-balancing approach to derive UK NH3 emissions for vital constraint of the existing Defra-used NAEI emissions. 

Outline PhD Plan

Year 1: Setup and test UK nested full chemistry TOMCAT configuration and compare with satellite NH3 products. Include detailed assessment of important satellite properties/errors (not accounted for in previous studies). 

Year 2: Implement and test the new portable UKCA sub-routines in TOMCAT and employ mass-balancing to derive new posterior UK NH3 emissions. 

Year 3: Extend new regional mass-balancing approach to derive high resolution, long-term monthly posterior NH3 emissions to investigate sources, seasonal cycles and post-2008 trends in NH3 emissions and AQ impacts (e.g. simulated aerosol formation and PM2.5). 

Year 4 (6-months): Write and submit PhD thesis and scientific publications. 

Training 

The student will gain training in using large satellite data sets, running atmospheric chemistry models and translating their research results into scientific publications. The student may also be able to join specialised training from Research Centres (e.g. NCAS) and DTP/CDT courses.

Entry requirements and how to apply

For more information, please see the project page on the University website.